1. Field of the Invention
This invention relates to a photoelectric sphygmomanometer of volume oscillometric method-type and, more particularly, to regulation of the quantity of light and gain of such a sphygmomanometer for a stable measurement.
2. Description of the Prior Art
In a conventional photoelectric sphygmomanometer of volume oscillometric method-type, measurement is performed after certain regulations are made. Specifically, when a cuff of the sphygmomanometer is being inflated, cuff-inflation is halted temporarily, the quantity of light is regulated and then the level of carrier wave pulsation is regulated so as to be maximized without being saturated within the dynamic range of an amplifier. The gain of pulsation following detection is also regulated so as to be maximized without being saturated within the dynamic range of a pulsation amplifier.
However, there are cases where the level of light received in such a sphygmomanometer changes owing to a variance in the transmission and absorption of light of a tissue of a living body. This variance can be ascribed to a change in the positional relationship between an artery and a light-emitting or light-receiving element, which can occur between the time of the regulation made during pressurization and the time at which blood pressure is measured at depressurization. The variance can also be ascribed to the color of the skin, etc. In such case, the carrier wave can saturate and surpass the dynamic range of the amplifier. A measurement cannot be taken until such saturation is eliminated.